1. Field of the Invention
The present invention generally relates to hand tools and, more specifically, to an adjustable safety utility knife with easily removable blade holder.
2. Description of the Prior Art
Utility knives are widely used in construction, business and hobby applications for cutting such materials as paperboard, wallboard, string and other objects. Commonly, such utility knives are in the form of an elongate hollow housing that can be gripped by the user along an intermediate portion thereof and into which there are placed trapezoidal flat cutting blades. The blades typically have a single cutting edge. The blade is typically slidably mounted between a retracted position within the housing and an extended position in which the cutting edge is at least partially exposed through a front end aperture or slot, the slot being coupled to a manually operated element, such as a button positioned in a manner convenient to be actuated by the user's hand.
Many utility knives include a region within the housing for storing one or two additional blades that can be used to replace the operative blade when it becomes dull. In most cases a screw or similar means is used for attaching the two clam shell members together during normal use. When blades are to be replaced, the screw is removed, allowing to two shell members to be separated, and access is provide to the replacement blades.
The flat cutting blades used in utility knives are most useful and are easiest to use when the blades are extremely sharp. These blades, therefore, are frequently replaced once they become dull. For this purpose, known utility knives provide storage within the handle for additional blades so that these will be readily available when needed. In order to facilitate this replacement procedure, some utility knives provide a blade holder which stores the plurality of blades and which can be quickly and conveniently removed from the utility knife handle. Examples of such holders are shown in U.S. Pat. Nos. 3,593,147; 3,872,591; 4,277,888; 4,761,882, 4,922,610; 5,005,290; 5,042,154; 5,386,632; 5,404,645; 5,604,984; 5,613,300; 5,644,843; and 5,727,320. However, these have the disadvantage that once the holder is removed from the handle, there is nothing to prevent one or more of the blades from falling out. However, because these blades have their edges exposed, this can create a hazardous condition for the user when one or more blades with exposed edges may need to be handled. See, for example, U.S. Pat. Nos. 3,593,417; 3,872,591; 5,386,632; 5,613,300; 5,644,843.
In U.S. Pat. No. 4,761,882, cutting blades are stored in a compartment at the rear of the handle housing, a transverse slot being provided in the handle for providing access to the replacement blades, which may be removed by pressing the exposed blade by a finger through the opening in the handle for removal of the blade through a slot at the rear of the handle. However, this utility knife requires that the storage compartment or magazine area be replenished by handling individual cutting blades and manual inserting them into the handle. Additionally, the provision of a relatively large finger opening exposes the interior of the handle cavity to exterior contaminants, including liquids, dust, etc., which may ultimately cause a deterioration of the internal operating components.
In U.S. Pat. No. 4,922,610, a blade holder having a magazine is disclosed in which the housing includes a slot the upper side thereof which allows a blade to be withdrawn by pivoting an operable device within the handle about a pivot in the blade magazine on which the respective blade is supported. However, with the disclosed blade removal device, only a small portion of the blade becomes exposed through the upper slot which may render the blade difficult to grasp and remove. Additionally, the angle at which the blade is positioned when in condition for removal such that it may contact other parts or components of the utility knife and, therefore, render removal more difficult or inconvenient.
In U.S. Pat. No. 5,404,645, a knife blade holder is disclosed in which the shell members are pivotally connected to each other to be movable in a scissors-like manner and a blade magazine is provided which can be inserted or withdrawn when the handles are pivoted relative to each other. However, when the handles are so pivoted, this also exposes the operative or active blade at the front end of the handle housing which can become dislodged and may need to be handled by the user.
Other utility knife designs are also known. Many of these use complex and costly constructions. For example, in U.S. Pat. Nos. 5,604,984 and 5,727,320, utility knives are shown with rotary blade magazines which substantially enlarged the back end of the utility knife handle and which make them less convenient to use. Additionally, the use of a rotary magazine requires a more complex construction, which significantly increases the cost of the unit.